1. Field of the Invention
The present invention generally relates to an image writing device, in which an image is written on an image bearing surface of a photoconductor moving in the sub-scanning direction and being repeatedly exposed along the main-scanning direction by using an exposure head where plural light-emitting elements are arranged in the main-scanning direction, an image forming apparatus including the image writing device, and an image writing method.
2. Description of the Related Art
An image forming apparatus employing an electrophotography method such as a copier, a printer, a facsimile machine, a digital multifunction peripheral, etc., has been widely used. The image forming apparatus employing the electrophotography method includes an image writing device that writes an image and forms an electrostatic latent image by exposing an image bearing surface of a photoconductor.
Then, the image forming apparatus develops the electrostatic latent image, which is formed on the image bearing surface of a photoconductor by the image writing device, with developer such as toner, etc., so as to form a toner image. The toner image is transferred onto a recording medium and is fixed thereon, and the recording medium, on which the fixed toner image is formed, is output from the image forming apparatus.
As the image writing device included in such an image forming apparatus, an image writing device employing a laser writing method (a raster optical system method) is mainly used. However, recently, more and more image writing devices employing a fixed writing method using the exposure head as described above have been used. As the exposure head, a light-emitting diode (LED) array is typically used where plural LED elements are arranged in the main scanning direction with a density in accordance with a resolution.
The image writing device that uses the LED array exposes a charged image bearing surface of the photoconductor by using light emission of the LED elements of the LED array to form the electrostatic latent image, so as to write the image. To that end, an LED array drive section controls the turning on and off of the LED elements of the LED array based on image data to be written. The image data are stored into a line memory on a main-scanning line basis, and are transferred to an LED array drive section in a line cycle corresponding to the resolution.
In the image writing device employing such a fixed writing method, it is desired to adjust an image writing start position in the sub-scanning direction, which is the moving direction of the image bearing surface, with high accuracy of less than or equal to one line cycle of the main scanning. To that end, there is a known method in which a line memory corresponding to plural lines are provided in a write control section, so that the timings of transmitting data from the line memory to the LED array are shifted from each other.
For example, Japanese Laid-open Patent Publication No. 2013-039798 discloses a technique in which a resist correction, which refers to the adjustment of the image writing start position in the sub-scanning direction, is performed with the high accuracy of less than or equal to the one line cycle of the main scanning. To that end, a method is employed in which the timings at which the pixel information is input from the line memory to the LED array are shifted from each other, and the timings of designating the read addresses of the line memory by a line memory control section, that is, the read timings are accordingly shifted.